Conventionally, sheet processing apparatuses include, for a folding process, a stopper and a dedicated path branching from a conveying path used to convey a sheet from an upstream device to a downstream device, and perform the folding process based on a so-called end-abutting in which a leading end of a sheet is caused to abut. That is, in the folding process, the sheet is caused to abut against the stopper in the dedicated path to adjust a folding position and form the deflected portion, and the deflected portion is nipped by a folding unit to fold the sheet.
JP2000-159433 discloses a folding structure with a reversible conveying roller pair without the stopper as shown in FIGS. 18A-18D. In FIG. 18A and FIG. 18B, a sheet is conveyed to a path with a conveying roller pair R1 and a reversible conveying roller pair R2. Next, in FIG. 18C, the sheet is bent by rotating the reversible conveying roller pair R2 in a reverse direction. Finally, in FIG. 18D, the bending part of the sheet is conveyed to the nip between a conveying roller R1a and a folding roller R3, and the sheet is folded.
However as shown in FIGS. 18C and 18D, the sheet with a first bending part F1 and a second bending part F2 is probably folded, when there is a space W2v between the conveying roller pair R1 and the folding roller R3. As such, a bending direction of the sheet is various and the sheet may not be folded at a desired position.